A repeater system (such as a distributed antenna system (DAS) or a single-node repeater) is typically used to improve the wireless radio frequency (RF) coverage provided by one or more base stations. The wireless service provided by each base station can include commercial cellular service or private or public safety wireless service. The repeater system can be implemented as an “active” system in the sense that the downlink and uplink RF signals are amplified before being repeated.
Active repeater systems can be used, for example, in sport stadiums, buildings (hotels, malls, or trade centers), metro stations and airports, trains, and tunnels. Each base station can be coupled to the repeater system via one or more cables or via a wireless connection, for example, using one or more donor antennas. Repeater systems can be used in other applications.
The capacity of each base station coupled to a repeater system can be dedicated to the repeater system. The capacity of each base station coupled to a repeater system can also be shared among the repeater system and a base station antenna system that is co-located with the base station and/or shared among the repeater system and one or more other repeater systems.
Each active element in each transmit signal path of the repeater system adds noise to the repeated RF signal transmitted from the signal path. Where the capacity of a base station is shared, it is desirable to configure the repeater system to avoid noise contribution at the receiver of the base station resulting from noise added by the active elements of the uplink transmit signal path of the repeater system. If the noise contribution at the receiver of the based station is too high, the receiver can be desensitized. Desensitizing the receiver of the base station can cause severe restrictions to a mobile communication system. For user equipment that is communicating directly with the base station (that is, not using the repeater system), desensitizing the receiver of the base station can result in a limited coverage area of the co-located base station antenna system, dropped connections, or throughput limitation.
Noise contribution at the receiver of the base station can be too high if the path loss (attenuation) between the repeater system and the base station is too low due to short distances between the donor antenna and the co-located base station antenna (for example, low free space loss), low coupling values between the repeater system and the base station (for example, where there is a cable connection between the repeater system and the base station). Noise contribution at the receiver of the based station can be too high if the noise figure (NF) of the repeater system is too high, if gain setting of the repeater system is too high (for example, resulting in amplified noise), or if multiple repeater systems share the capacity of one base station.
To avoid noise contribution at the receiver of the base station, proper repeater system design and configuration is necessary. However, for some use scenarios, avoiding such noise contribution solely by proper repeater system design and configuration may not be possible due to technical and geographical limitations or the need for multiple repeater systems share the capacity of the same base station. In such scenarios, it is helpful to eliminate noise added by the active elements in the uplink signal path of the repeater system by using a “squelch” feature to “mute” the uplink signal path. When the uplink signal path is muted, the repeater system does not transmit a repeated uplink RF signal to the base station or transmits a repeated uplink RF signal at a relatively low amplification level. This can be done when there are no UEs within the coverage area of the repeater system and the repeater system is not needed. This can occur, for example, where a repeater system is deployed in a building that is not occupied during nighttime or where a repeater system is used to improve the coverage of public safety wireless service during emergency situations only.
However, generally, such a squelch feature is implemented using a digital signal processing (DSP) unit that analyzes the uplink signals received from the UEs. This is required to guarantee a response time for switching from a muted state to an unmuted state that is sufficiently fast (for example, within microseconds) to avoid cutting the signal and risking losing connections. Wireless communications standards like Global System for Mobile Communications (GSM) and Terrestrial Trunked Radio (TETRA) are the main driver for such fast response times and hence for costly DSP-based squelch implementations.